Intravascular devices such as embolic protection filters are generally placed in a body lumen such as an artery or vein, downstream of a therapeutic site to filter emboli contained in the blood. In a typical procedure such as percutaneous transluminal coronary angioplasty (PTCA), an embolic protection filter is loaded into a delivery device such as a catheter or sheath, and advanced along a guidewire in a collapsed position to a location downstream a lesion. Once positioned downstream the lesion, the embolic protection filter is ejected from the delivery device and deployed in the blood vessel. An angioplasty catheter containing an angioplasty balloon is then advanced along the guidewire and positioned across the site of the lesion to be dilated. The angioplasty balloon is then inflated, forcing the lesion to rupture and dislodge from the wall of the vessel. The dislodged debris is then carried downstream towards the embolic protection filter, where it can be collected and stored for later removal.
A number of embolic protection filters have been developed to filter embolic debris contained in the blood stream. Typically, these devices contain a support structure coupled to a filter membrane that filters contaminants in the blood stream. The support structure generally includes a number wires, ribs, or struts forming a filter frame that supports the filter membrane in an expanded position within the vessel. As the embolic debris passes through the mouth of the filter, it is deposited along the inner wall of the filter membrane, typically at a location distal the mouth of the filter at or near the apex of the filter. At the conclusion of the therapeutic procedure, the filter frame is then collapsed within a retrieval catheter and removed from the vessel.
As the filter frame is collapsed, the generally laminar flow of blood in the vessel may be temporarily disturbed, resulting in a turbulence spot at or near the mouth of the filter. A slight backpressure may result, causing the captured embolic debris to flow upstream towards the mouth of the filter. In some situations, the amount of embolic debris collected in the filter membrane may affect the downstream perfusion of blood through the filter, drawing the embolic debris proximally towards the mouth of the filter. As a result, some of the filtered embolus may escape from the filter and reenter the blood stream.